1. Field of the Invention
The present invention relates to a method of producing a stator for a variable capacitor, and more particularly, to a method of producing the stator including a polishing step. Further, the present invention relates to a variable capacitor including the stator produced by the above-described production method.
2. Description of the Related Art
A conventional variable capacitor is described in Japanese Unexamined Patent Publication Application No. 11-87173. FIGS. 4 to 6 show the variable capacitor described in this Unexamined Patent Publication Application No. 11-87173.
FIG. 4 is a perspective view of a variable capacitor 1. FIG. 5 is a perspective view of the variable capacitor 1 of FIG. 4, taken from below the variable capacitor 1. FIG. 6 is a cross-sectional view of the variable capacitor 1 shown in FIG. 4.
The variable capacitor 1 includes a stator 2, a rotor 3, and a cover 4 which define the capacitor 1.
In particular, the stator 2 is made of a ceramic dielectric, and has first and second main surfaces 21 and 22 which are parallel to each other, and a side surface 23 connecting the first and second main surfaces 21 and 22. Moreover, stator electrodes 5 and 6 are arranged inside of the stator 2 to extend parallel to the first and second main surfaces 21 and 22, respectively. Stator terminals 7 and 8 are made of conductive films and extend on a portion of the side surface 23, and more particularly, on the outer end-surfaces of the stator.
The two stator electrodes 5 and 6 and the two stator terminals 7 and 8 are provided as described above, such that the structure of the stator 2 is symmetrical, and accordingly, it is unnecessary to consider the direction of the stator 2 when the variable capacitor 1 is produced. In the capacitor 1 illustrated in FIGS. 4 and 6, the stator electrode 5 and the stator terminal 7 operate, while the stator electrode 6 and the stator terminal 8 do not operate.
On the main surface 22 of the stator 2, a rib 9 is arranged to extend longitudinally through the approximate center portion of the main surface 22.
The rotor 3 is made of conductive metal, and is provided on the first main surface 21 of the above-described stator 2. On the underside of the rotor 3, a substantially half-circular rotor electrode 11 with a protuberant step-portion is provided. Moreover, on the underside of the rotor 3, a protuberance 12 having the same height as the rotor electrode 11 is provided, and inclination of the rotor 2 is prevented due to the present of the rotor electrode 11. The rotor 3 is provided with a driver recess 13 to receive a tool, such as a driver or other suitable tool with which the rotor 3 is rotation-operated.
The cover 4 is made of conductive metal, receives the rotor 3, and is fixed to the stator 2. The rotor 3 is held by the cover 4 and is rotatable with respect to the stator 2.
In the cover 4, an adjustment hole 14 is provided to expose the driver recess 13 of the rotor 3. In the periphery of the adjustment hole 14, a spring action portion 15 is provided which is in contact with the rotor 3 and presses the rotor 3 against the stator 2. The spring action portion 15 is inclined downwardly at the periphery of the adjustment hole 14, toward the center of the adjustment hole 14, and moreover, is provided with a plurality of protuberances 16.
Moreover, the cover 4 is provided with engagement pieces 17 and 18 extending downward in opposition to each other. The engagement pieces 17 and 18 are bent to engage with the main surface 22 of the stator 2, and thereby, the cover 4 is fixed to the stator 2. The above-described rib 9 provided for the stator 2 protrudes the same amount as the engagement pieces 17 and 18 bent onto and along the second main surface 22 of the stator 2, such that the variable capacitor 1 is stably and securely mounted on an appropriate wiring substrate (not shown).
Furthermore, on the cover 4, a rotor terminal 19 is provided and extends downward.
In the variable capacitor 1 having the above-described structure, the rotor electrode 11, which is in contact with the first main surface 21 of the stator 2, is opposed to the stator electrode 5 via a portion of the ceramic dielectric defining the stator 2, and thereby, a static capacity is produced. The rotor 3 is rotationally operated to vary the effective opposition area of the rotor electrode 11 opposed to the stator electrode 5 to change the static capacity. The adjusted static capacity is drawn between the stator terminal 7 electrically connected to the stator electrode 5 and the rotor terminal 19 provided on the cover 4 in contact with the rotor 3 having the rotor electrode 11 provided thereon.
In the above variable capacitor 1, to increase the maximum static capacity and obtain a stable static capacity, the first main surface 21 of the stator 2 is polished such that the thickness of the dielectric between the main surface 21 and the stator electrodes 5 and 6 is reduced, and the main surface 21 in contact with the rotor electrode 11 is smoother.
Moreover, the first main surface 21 of the stator 2 is polished for the following additional purpose.
The conductive films defining the above-described stator terminals 7 and 8 are formed, e.g. by dipping the respective end portions of the stator 2 into a bath including a conductive paste having a desired thickness to apply the conductive paste to the respective end portions of the stator 2, and then, baking the paste. Thus, the conductive films are provided not only on the side surface 23 of the stator 2, but also extend from the side surfaces 23 onto a portion of the first and second main surfaces 21 and 22.
However, in the variable capacitor 1, as shown in FIGS. 4 and 6, the stator terminals 7 and 8 do not extend on the first main surface 21 of the stator 2. Thus, to obtain this configuration of the stator terminals 7 and 8, after the conductive films are formed as described above, the first main surface 21 of the stator 2 is polished such that the conductive films on the first main surface 21 are removed.
The upper ends of the stator terminals 7 and 8 can be positioned at a relatively large distance from the edge of the cover 4 or the peripheral surface of the rotor 3 by preventing the formation of the stator terminals 7 and 8 on the first main surface 21 of the stator 2 as described above.
Accordingly, if an error in positioning of the rotor 3 and the cover 4 with respect to the stator 2 occurs when the variable capacitor 1 is produced, or a deviation in position of the cover 4 and the rotor 3 is generated when the rotor 3 is rotated, short-circuiting and deficient withstand voltage will not occur between the edge of the cover 4 and the upper end portions of the respective stator terminals 7 and 8, or between the peripheral surface of the rotor 3 and the upper end portions of the respective stator terminals 7 and 8.
When the first main surface 21 of the above-described stator 21 is polished, conventionally, the plurality of stators 2 are simultaneously processed to improve the efficiency of the polishing process.
FIGS. 7A to 7D illustrate a conventional polishing method used to achieve the above-described polishing. It should be noted that FIGS. 7A to 7D are also used for illustration of the problems to be solved by the present invention, as described later.
FIGS. 7A to 7D schematically show the stators 2 shown in FIGS. 4 to 6, and the elements in FIG. 7 corresponding to those in FIGS. 4 to 6 are designated by the same reference numerals. Moreover, stator components defining the stators 2 are designated by reference numeral 2a in FIG. 7.
The plurality of stator components 2a are prepared as shown in FIG. 7A. In each of the stator components 2a, the stator terminals 7 and 8 made of conductive films are arranged to extend from the side surface 23 onto a portion of the respective first and second main surfaces 21 and 22.
The plurality of stator components 2a are supported on the holding surface 26 of the holder 25 as shown in FIG. 7B. Each of the stator components 2a is positioned such that the second main surface faces the holding surface 26. To fix each of the stator components 2a to the holding surface 26, pressure-sensitive adhesion is applied.
Next, the first main surfaces 21 of the plurality of stator components 2a, while the components 2a are supported by the holder 26, are polished by a polishing plate 27, as sequentially illustrated in FIGS. 7B and 7C.
FIG. 7D shows the plurality of stators 2 obtained by polishing the stator components 2a. 
However, in the above-described polishing method, as shown in FIG. 7D, in some instances, the plurality of stators 2 have different thicknesses between the first main surfaces 21 and the stator electrodes 5 and 6. This causes variations in maximum static capacity of the variable capacitors 1.
The above-described variations are caused by the variations in thickness of the stators 7 and 8. In particular, as shown in FIG. 7B, the plurality of stator components 2a are supported by the holder 25 while the stator terminals 7 and 8 are in contact with the flat holding surface 26. Accordingly, the differences in thickness between the conductive films defining the stator terminals 7 and 8 cause differences between the positions of the first main surfaces 21 of the stator components 2a. As a result, in the plurality of stators 2 obtained by polishing the stator portions 2a with the polishing plate 27, variations in thickness between the first main surfaces 21 and the stator electrodes 5 and 6 occur.
Moreover, as shown in FIGS. 7A to 7D, when the conductive films defining the stator terminals 7 and 8 are excessively thin, as shown in the stator component 2a or stator 2 which is the second from the left side of the arranged components or stators, the polishing plate 27 does not contact the first main surface 21 of the stator component 2a, shown in FIG. 7C. Therefore, in some cases, the stator terminals 7 and 9 on the first main surface 21 are not completely removed, as shown in FIG. 7D.
Moreover, according to the polishing method illustrated in FIGS. 7A to 7D, if there is a difference in thickness between the conductive films of the two stator terminals 7 and 8 of each stator components 2a, the component 2a encounters the problem illustrated in FIGS. 8A and 8B. FIGS. 8A and 8B correspond to FIGS. 7C and 7D, respectively.
As shown in FIG. 8A, if the conductive film for constituting the stator terminal 7 is thinner than that for constituting the stator terminal 8, the stator portion 2a is held in an inclined posture on the holding surface 26 of the holder 25. Accordingly, the stator portion 2a is polished by means of the polishing plate 27 while the portion 2a is in this inclined posture.
As a result, in the produced stator 2, the first main surface 21 formed by polishing is not parallel to the second main surface 22, and similarly, is not parallel to the stator electrodes 5 and 6, as shown in FIG. 8B.
If the above-described stator 2 is used in the variable capacitor 1, the rotor 3 does not rotate stably, and moreover, the static capacity is unstable.
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide a method of producing a stator of a variable capacitor, and a variable capacitor including the stator produced in the production method.
The method of producing a stator of a variable capacitor in accordance with preferred embodiments of the present invention includes the steps of preparing the stator for use in the variable capacitor which is made of a dielectric, has first and second main surfaces which are parallel to each other, and a side surface connecting both of the first and second main surfaces, the stator provided with a stator electrode extending in parallel to the first and second main surfaces, the stator electrode arranged opposite a rotor electrode provided on a rotor through at least a portion of the dielectric, the rotor electrode rotatably supported in contact with the first main surface, and a stator terminal provided on at least a portion of the side surface to be electrically connected to the stator electrode, preparing a stator component which defines the stator and is provided with the stator electrode and the stator terminal, the stator terminal being made of a conductive film and extending from the side surface onto a portion of the respective first and second main surfaces, and a protruded portion provided on the first main surface where the conductive film defining the stator terminal is not provided, the protruded portion being provided such that the height at the top surface of the protruded portion is greater than the thickness of the conductive film, and polishing the first main surface of the stator component having the top surface of the protruded portion as a reference to remove the portion of the conductive film extending on the first main surface.
Preferably, the above-described step of polishing includes the steps of holding the plural stator components with a holder to arrange the top surfaces of the protruded portions on the same plane; and polishing the first main surface of the stator components while the plural stator components are held by the holder.
More preferably, the step of holding the plural stator components with the holder includes the steps of preparing an arrangement member having a flat arrangement surface, arranging the plural stator components using the arrangement member with the top surfaces of the protruded portions being in contact with the arrangement surface of the arrangement member, preparing a polishing fixing agent to fix the stator components to the holder, and fixing the second main surfaces of the plural stator components to the holder through the polishing fixing agent.
Particularly, the method of producing a stator for use in a variable capacitor in accordance with the present invention is advantageously applied when the stator has the stator electrode provided inside the dielectric.
Moreover, the method of producing a stator for use in a variable capacitor in accordance with the present invention is advantageously applied when the conductive film defining the stator terminal is formed by applying conductive paste to extend from the side surface onto a portion of the respective first and second main surfaces, and then baking the paste.
Moreover, the present invention is intended for a variable capacitor including the stator produced in the above-described method.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments thereof with reference to the drawings.